<!DOCTYPE html>
<html>
<body>
<style>
  html, body, div {
    margin: 0;
    padding: 0;
  }
  div {
    width: 75px;
    height: 75px;
    float: left;
  }
</style>

<div style="background-color:red"></div>
<div style="clear:left"></div>
<div style="background-color:blue"></div>

</body>
</html>